This invention generally relates to anodes for alkaline electrolysis and more specifically to methods of making a catalytic anode for alkaline electrolysis.
Electrolysis of alkaline solutions for production of hydrogen is receiving increased attention with society moving towards a hydrogen economy. This technology is known and has been studied for a long time and is suited for large-scale unattended operation. However, there are known issues with the process. The effectiveness of the method reduces over time due to development of overpotentials at the cathode and the anode. Overpotential at the anode—the oxygen electrode—constitutes a significant part of the total cell overvoltage and in turn represents a major energy requirement of electrolysis.
There have been multiple attempts to reduce anodic overvoltage. Initial attempts deployed noble metal electrodes like platinum. Although, platinum provides good catalytic activity, the cost becomes prohibitive for large-scale units. Another choice of material is nickel as a base material for the anode because of its stability in the alkaline environment. Typically a porous electrode is employed because it affords higher surface area for oxygen evolution. Initially the nickel electrodes are plated with platinum group metals. This combination results in lower loading of platinum, leading to reduction in cost while retaining the catalytic activity. But still the cost for industrial sized equipment is too high. The next generation of anodes incorporates various non-noble metal coatings onto the electrode. This includes nickel oxide and spinel oxides, for example, that acted as electrocatalysts and reduce the electrode overpotential levels. These oxides are typically deposited by techniques like electrodeposition (plating), slurry deposition, or spraying techniques like vacuum spraying or arc spraying. All these methods need special surface preparation and elaborate manufacturing process steps, resulting in higher costs of making electrodes and the electrolyzer assembly.
It is therefore desirable to devise a simple, cost effective method to produce oxygen electrodes (anodes) for alkaline water electrolysis.